Speaking off the cuff, I'm not sure that nations can be strictly, or even mostly, defined by their ethnicity. I would need to do some numbers to say anything more formally, but I constantly come back to Israel, Rome, Turkey, even China, where the "nation" had such imminent prestige that myriad ethnicities took on its "nationhood" upon entering/invading/outbreeding even while having zero common parentage with the founders. Did the meta-nations lose something in the process? Sure. Did they endure? I'd say yes. Your nation doesn't necessarily stop because its people are suddenly able to sprout fantastic moustachios. But boy, is that a sore topic. It might actually be the sorest.

Great piece, btw.